Metal cans or containers, such as aluminum cans to contain beverages, are commonly manufactured by drawing and ironing a circular metal blank into a cylindrical can body having a side wall and a bottom wall. Such cans are then fed into necking and flanging apparatus by transfer or star wheels. Each can enters one of a number of stations in a necking turret undergoing rotational movement which is synchronous with the continued movement of the cans in the star wheel. During this rotational movement, the peripheral edge portion of the can side wall is formed by annular die members or spin forming members to form a neck of reduced diameter at the open end of the can. The necked cans are then transferred via transfer wheels to a flanging turret where the open edge of the can is flanged into a radially outward directed flange suitable for later receiving a can end in a known manner. The arrangement of drawing and ironing machines for forming the can bodies, and machines containing necking and flanging turrets are well known in the art.
A plurality of flanging heads are typically circumferentially spaced at the periphery of the flanging turret. Each flanging head has plural flanging rollers or spinners freely rotatably supported about their respective longitudinal axes in a central housing or cage. The cage is rotatable about its central longitudinal axis so that the flanging rollers revolve therearound in planetary relationship during flanging. Each flanging head typically includes an outer housing formed with a mounting flange adapted to be bolted to a mounting disk attached to the flanging turret, as is well known. The central housing containing the flanging rollers is rotatably disposed in the outer housing with ball bearings. A splined shaft projecting rearwardly from the outer housing is attached to the central housing to impart rotational movement about the central longitudinal axis via meshing contact with gearing disposed within the flanging turret.
The front of the flanging head is defined by a stop ring 100 (depicted in prior art FIG. 1) bolted to the outer housing. A retainer plate sandwiched between the stop ring and ball bearing elements assists in maintaining the forming surface 120 of each flanging roller 140 in operative alignment with the stop surfaces 160 on the stop ring 100. As the flanging heads rotate, the marginal necked free edge portion 180 of the can is advanced into contact with the rotating cluster of flanging rollers 140. Since the can does not rotate, contact between the marginal end 180 with the revolving rollers 140 induces free rotation of each roller which results in spinning contact and flange formation as the open end of the can contacts the progressively larger diameter portions 200 of each roller. These progressively larger diameter portions 200 cause corresponding enlargement of the can end and deflection of the metal into a flange 220 extending approximately perpendicular to the longitudinal axis of the can.
As the formed flange 220 is in its final forming stages during final camming movement of the can against the rotating rollers 140, the flange end contacts the stop surfaces 160 of the stationary stop ring 100, whose purpose is to stop the flange 220 at a specific preselected diameter so that the flange has the same width along all sides of the can. In practice, however, the annular flange 220 usually strikes one side of the surface 160 before it hits all sides. When this happens, it usually takes only a small additional force to disadvantageously force the flange into the crack 240 formed between the rotating roller 140 and the stationary stop ring 100. When this occurs, the can is ruined and must be scrapped, since the metal forced into the crack 240 forms a sharp vertical ear on the can flange 220.
FIG. 2 is an illustration of a flanging roller and stepped stop ring arrangement which overcomes this problem, as disclosed in U.S. Pat. No. 5,235,839, to Lee, Jr. et al, assigned to Reynolds Metals Company, Richmond, Va., the assignee of the present invention. Therein, an apparatus for flanging cans includes a flanging head assembly having a cluster of freely rotatable spin flange rollers 12 and a stop ring 26 against which the flange 66 hits during the final flange forming stages to limit the flange to a specific diameter. To prevent the flange 66 from entering a crack formed between each rotating roller 12 and the stationary stop ring 26, there is provided a step 102 spacing the stop ring surface 70 from the roller forming surface. In this manner, as the terminal edge 68 of the flange 66 slides around the flanging roller 12 during final forming, it will pass over the crack 72 and across the step 102 to lodge in a corner 85' formed between the step and stop ring surface. The step 102 is preferably a conical surface extending from the stop ring surface 70 in a direction away from the can bottom. This conical surface extends radially inwardly a sufficient distance to contact unsupported flange portions 110 between the flanging rollers 12 to limit the degree of elastic sagging of these portions. The relevant disclosure of U.S. Pat. No. 5,235,839 is incorporated by reference herein in its entirety.
The stop ring flanger depicted in FIG. 2 does an excellent job in flanging the free edge portions formed in can bodies, particularly those can bodies formed by a process known as spin flow necking such as disclosed in U.S. patent application Ser. No. 07/929,933, filed Aug. 14, 1992, also assigned to Reynolds Metals Company, Richmond, Va., the assignee of the present invention. Spin flow necking is a process of necking in an open end of a metal can to provide an outwardly flared open end which is then flanged, such as with a flanging apparatus as disclosed in the '839 patent, to allow a can end to be seamed thereto after filling.
The flanging apparatus of the '839 patent does an excellent job in reforming both the spin flow and other types of necked-in cans to produce a uniform plug and a uniform flange width from cans that have a wide variety of flange widths and plug diameters prior to flanging. However, there is another dimensional variation that shows up in all cans, including spin flow cans, which is a variation in the trim or pre-necked can height. This variation can be allowed for in the flanging apparatus by utilizing a spring-loaded base pad assembly which is pre-loaded to a predetermined spring force that is necessary to flange the can without creating an excessive flanging force.
With reference to FIG. 3, the spring-loaded base pad assembly 150 is generally comprised of a base pad 152 adapted to contact the can bottom 154, and a spring pad adjusting collar 156 interconnected to the base pad through a plurality of springs 158 having a predetermined spring force. A spindle or shank mechanism 160 is connected to the spring pad adjusting collar 156 and is cam controlled in a known manner to axially advance the open end 162 of the can body 164 in a forward stroke of the spindle 160 into flanging contact with the flanging rollers 12 by advancing the base pad 152 with the can bottom 154 seated thereon through the collar 156 and springs 158. The base pad assembly 152 is set so that when a can 164 of minimum height is flanged, the spring force is sufficient to flange the can and the spring-loaded base pad 152 may or may not be deflected rearwardly towards the spring pad adjusting collar 156. The shank or spindle mechanism 160, as mentioned above, is cam operated and adjusted to a forward position so as to apply this spring flanging force on the can.
When a spin flow can that is formed towards the maximum of the manufacturing tolerance range is flanged, the same spring force is required. However, this spring force tends to be reached slightly before the shank mechanism 160 has reached the forward end of its working stroke. This spring-loaded base pad 152 compensates by moving back a small amount (relative to the shank) against the predetermined spring force to allow the can to be flanged without applying unnecessarily high forces.
The combination of the stepped stop ring and the spring-loaded base pad do an excellent job in producing cans of high quality and consistency. However, a spin flow can is sometimes produced which, as a result of an improper adjustment or slippage in the spin flow necking mechanism or unusual metal properties or heat treatment of the can, has a larger than normal flange width, or plug diameter, or both. This type of can will usually first contact the stationary stop ring 26, as depicted in FIG. 4, instead of first contacting the spinning flanging roller forming surfaces 66a and then being forced to contact the stationary stop ring by the rotating spinner as depicted in FIG. 2. The shape of the can open end as depicted in FIG. 4 has a wide flaring flange 170 of about 60.degree. from an axis L (parallel to the can longitudinal axis) which lodges into the corner 85' of the stationary stop ring 26. The shape of the partial flange on the can is such that it misses contacting the rotating spinners 12 entirely, or at best has only minimal contact with the tips of the forming surfaces on the spinners. As a result, the flared open end on the can is supported by the stationary stop ring 26 and is exceedingly strong to the point of overcoming the predetermined spring pre-load force of springs 158 which is generally set to be about 75-110 pounds. The flange depicted in FIG. 4 can support loads of about 150-200 pounds. The can is therefore sufficiently strong to overcome the pre-loaded springs 158 and thereby prevents the base pad 152 from completing its normal range of movement while allowing the shank mechanism 160 to complete its working stroke without reforming the can. As a result, the spin flow can passes through the flanging apparatus without being reformed. This can may end up on the finished can pallet and be shipped to a customer without being able to be seamed properly on a seamer. As a result, a filled can may be produced that could leak product at a later time.
It is accordingly one object of the present invention to provide an apparatus which ensures that all cans are manufactured with a uniform flange width and plug diameter.
Another object of the invention is to minimize the occurrence of improperly flanged cans from being filled and seamed in a manner that may subsequently produce product leakage.
Yet a further object is to provide a simple design modification to a flanging apparatus having a spring-loaded base pad to ensure proper flange forming.